Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Heart valve – Having rigid or semirigid pivoting occluder
Reexamination Certificate
2002-04-25
2004-03-02
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Heart valve
Having rigid or semirigid pivoting occluder
C623S002200, C623S002270, C623S002340
Reexamination Certificate
active
06699283
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED R & D
Not applicable.
REFERENCE TO SEQUENCE LISTING
Not applicable.
BACKGROUND
1. Field of Invention
The present invention relates to mechanical heart valve prostheses, and, in particular, to a bileaflet prosthetic heart valve with a rectangular orifice and periphery that enable full leaflet opening for improved blood flow with a single central orifice.
2. Description of Prior Art
A wide variety of heart valve prostheses have been developed to operate hemodynamically in conjunction with the pumping action of the heart to replace defective natural valves. These valves generally have annular valve bodies that function with a single occluder or a plurality of occluders that allow forward blood flow through the valve during systole and prevent retrograde flow during diastole.
The first successful mechanical heart valves were caged ball valves, pioneered by Starr and Edwards, based on the ball valve of U.S. Pat. No. 19,323 (Williams, 1858). The hemodynamic concept of the single tilting disk valve is an improvement over the caged ball valve because it reduces energy loss, and therefore it largely replaced the caged ball implant. U.S. Pat. No. 3,546,711 (Bokros, 1968) discloses a single tilting disk heart valve with journaled hinges set away from the orifice wall. U.S. Pat. No. 3,835,475 (Child, 1974) discloses a free-floating disk that is constrained by projections. U.S. Pat. No. 4,306,319 (Kaster, 1981) discloses a tilting disk heart valve with an oval, egg, or kidney shaped disk and orifice. In this valve, the disk is hinged with an axis of rotation across the largest dimension of the orifice. The tilting disk heart valves have improved flow characteristics over the caged ball valves, but still partially obstruct the central flow of blood while open.
Bileaflet valves were designed to be an improvement over the tilting disk valves; they open more smoothly, close more reliably, and have a lower profile. U.S. Pat. No. 4,078,268 (Possis, 1976) discloses a bileaflet valve with hinge axes slightly offset from the orifice diameter. U.S. Pat. No. 4,159,543 (Carpentier, 1976) discloses a bileaflet valve with diametric hinge axes in which the leaflets rotate about physical axles. U.S. Pat. No. 4,276,658 (Hanson, 1980) discloses a manifestation of a bileaflet valve where the leaflets have convex ears that fit into concave sockets for pivoting. U.S. Pat. No. 4,352,211 (Parravicini, 1981) discloses a design in which the leaflets are arcuate cylindrical shells contoured to match the round aortic duct. U.S. Pat. No. 4,451,937 (Klawitter, 1982) discloses a design with ear-guided hinges, in which the leaflets are constrained by protuberances. U.S. Pat. No. 4,655,772 (De Liotta, 1985) discloses a bileaflet design in which the leaflets are mounted on hook guides. The shift from the caged ball or tilting disk valve designs to the bileaflet designs was an improvement in safety, efficacy, and efficiency. However, bileaflet valve designs still partially obstruct the blood flow when the leaflets are open.
In an effort to decrease central occlusion, trileaflet valves have been developed. U.S. Pat. No. 4,820,299 (Phillippe, 1986) discloses a trileaflet design with hinge axes disposed from the center of the orifice at a distance that is 75 percent of the radius of the base. U.S. Pat. No. 5,207,707 (Gourley, 1993) discloses another trileaflet valve with ear-guided leaflets and conical stops. U.S. Pat. No. 5,628,791 (Bokros, 1997) discloses a trileaflet valve with another design for the hinge guidance projections. U.S. Pat. No. 5,843,183 (Bokros, 1998) discloses a trileaflet design with projection stops, as well as a significantly orifice-reducing contour to provide additional stops. U.S. Pat. No. 6,059,826 (Bokros, 2000) discloses a design with tapered leaflets to reduce cavitation in the blood.
U.S. Pat. No. 3,938,197 (Milo, 1976) discloses a valve with a pentagonal orifice mounted in a circular ring and five roughly triangular leaflets. This valve has no central occlusion, but has a significantly reduced orifice area as well as an excess of moving parts.
A major drawback of existing mechanical heart valves is the risk of thrombus formation on the valve that can foul the mechanism. Additionally, such thrombi can embolize and lead to medical conditions such as stroke, heart attack, and pulmonary embolism. Thrombosis occurs when blood is damaged by shear forces on blood corpuscles, by turbulent flow, or by chemical interactions with synthetic materials, all of which are exacerbated by cardiovascular implants. Presently, mechanical heart valve recipients receive anticoagulant drug therapy in order to avoid thrombus formation; however, this drug therapy introduces a new set of comparable health risks. Reducing the blood damage caused by the valve has the benefit of lowering the required levels of anticoagulants needed to prevent thrombosis.
Shear forces and turbulence are generated as a result of a velocity gradient in the fluid flow. In unobstructed ducted flow, the fluid velocity is a maximum in the center of the duct, and is zero at the boundary. If the occluder mechanism of a valve lies in the central region of flow when the valve is open, its surfaces induce drag on the high velocity fluid causing additional shear forces and turbulence in the fluid. With the exception of U.S. Pat. No. 3,938,197 (Milo, 1976) this is the case in all of the heart valve designs in the prior art listed above. Some valve designs move the occluders out of the direct center of flow when the valve is open by employing three or more leaflets; however, there is still significant flow occlusion. Additionally, these designs increase the number of moving parts, which, in turn, increases the probability of mechanical failure.
The use of synthetic materials such as pyrolytic carbon that have high durability and reasonably low thrombogenicity is known to the prior art. Such materials have effectively minimized material-induced thrombosis.
SUMMARY
In accordance with the present valve, a heart valve prosthesis comprises an annular body that encloses an orifice that is generally rectangular in cross-section and leaflets that open to allow forward blood flow and close to prevent retrograde flow. The axes of rotation of the leaflet hinges are near the periphery of the orifice.
Objects and Advantages
Accordingly, the primary objects of this valve are: first, to remove central flow obstructions in the valve orifice through geometric optimization; second, to obviate the need for small side orifices that split flow; third, to maximally size leaflets, limiting the required number to two; and fourth, to maintain orifice area by obviating irregular leaflet contours, taking advantage of the uniform geometry of the rectangle. These objects result in numerous advantages, detailed below, which provide a superior flow dynamic compared to the prior art. This superior flow dynamic reduces stress placed on the heart and damage to the blood, which, in turn, reduces the burden of anticoagulation therapy and the risk of thrombosis to the patient.
There are guidelines that can be used to evaluate and compare valve designs. The primary four design principles for replacement heart valves are: (1) energetic efficiency, (2) embolism prevention, (3) reduction of turbulence, and (4) reduction of blood trauma. Other principles such as noise reduction, sterilization, and material biocompatibility have largely been standardized.
These four principles deal with reducing damage to the heart (1) and blood (2-4). The major drawback of mechanical valves, vis a vis bioprosthetic valves, is that patients require anti-coagulation therapy. The dosage and frequency of this treatment attempts to minimize the competing morbidity and mortality due to stroke (too little anti-coagulant) and due to hemorrhage (too much anti-coagulant). The present valve is based on the realization that placing the leaflets in a central location has deleterious effects on all four design principles, which stem from one central cause: dividing blood flow.
Comparing
Hartemink Christopher Allan
Mazzucco Daniel Clarke
Newburg Seth Owen
Miller Cheryl
Snow Bruce
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